Wednesday, March 18, 2015

Ken, 148x12, the future, Keanu Reeves

As promised, here's part 1 of my thoughts, musings, ramblings... incoherent gibberish about new axle standards.

I'm not even going into the new 110x15 fork standard right now, we'll concentrate on 148x12.

First, remember: if you are buying a hardtail, a through axle has no actual benefit over a QR unless you weigh 400 pounds or are constantly forgetting to tighten your skewer. Your pathetic excuses for legs won't get any more power to the ground than they did before - the rear end of a hardtail really doesn't flex much, so adding a big fat axle make zero difference in how the bike rides. Of course, I build them all the time, and if/when I get around to building myself a new bike, that's what I'll do. Why? Because time marches on, and it's harder and harder to get nice QR parts - just like it's hard to find a really nice set of v-brakes these days. C'est la vie. Take the red pill. Or maybe the blue one? I can't remember, the sequels have caused me to block all Matrix-related knowledge from my brain to avoid the pain.

142x12 came out about 3 years ago and quickly took the world by storm. Why? It promised a bit stiffer rear ends on FS bikes, compatibility via adapter for most existing hubs as the cassette and disc rotor stayed in exactly the same place, and something new to sell to the bike-buying public. Which I would roundly condemn, except that I'm one of the purveyors of said new stuff.

27.5+? My doing.
As a giant world of diverse wheel/tire and drivetrain options has opened up in the post-29er glasnost, lots of manufacturers realized that cramming 3x29/27.5" tires into frames built around 73mm BB shells and 50mm chainlines (just a quick pause for a definition here: "chainline" here means the distance from the center of the frame to the center of the middle chainring, though these days that mostly means the *only* chainring. Here's Sheldon Brown's definition) would cause some terrible problems fitting everything where it needed to go. The chainstay, tire, and chainring all fight for space on a typical mountain bike frame (FS or hardtail) and if you have to give too much to the tire - you've either gotta lengthen the chainstays or do *something* to move the chainring out of the way. As more and more gears get crammed onto cassettes, the flanges of the hub have also gotten closer together (this has been going on for 20 years, really) which is generally bad, as the spoke tension between driveside/non driveside gets out of whack and the wheel gets less laterally stiff and weaker. Bigger rims (ie 27.5, 29) exaggerate these problems. Something had to give (well, ok, maybe "had" is too strong a word). Something is giving, anyway.

Enter "Boost" (why didn't 142x12 get a cool name?) 148x12 rear ends. The idea here is that you move both the cassette and disc rotor outboard 3mm, and move the flanges out to match. Result, you can move the *chainring* out a bit to make more room for the tire, keep a decent chainline, and end up with a bit stronger rear wheel to boot.

Now, there's another solution out there that I've been doing for over a decade along with a few other weirdos. It's to stick with 135x10 (or now142x12) spacing, but move the *entire* rear end (meaning, the hub/dropouts/stays) about 5-10mm to the driveside (the exact amount depending on application). This gives you a great chainline for single ring bikes and loads of room for short chainstays and big tires. It's also a near-dishless/even tension rear wheel. Great stuff, IMO. Cannondale ripped me off this year with their "AI system" (here's C'dale's explanation of the setup). Stupidmobile (you know, the 29er with 40cm chainstays?) was built this way. So are many bikes I build for customers, because it gives you a ton of benefits and really only has a few drawbacks. You can also do fun stuff like an 83mm low-q-factor fatbike by using various amounts of rear end offset (Felix's runs a 135x10 rear hub offset 10mm).

Whew. Did that all make sense? No? That's what I run into a lot. Many people don't like the idea of asymmetry, so the whole idea is off the table. I think that's a big part of the 148x12 idea - easier to explain, inherently less weird and threatening...but we don't do normal and unthreatening around here!

Ken wanted it *all*. 148x12, lots of tire clearance (in his case 27.5x2.8-3 or so) and short, short chainstays (well, not totally insane - we did 41.5cm). So we went nuts and did an *offset 148x12* setup. In this case, it's just 2mm of offset to get the chainline we wanted, but it still felt weird to take a brand new Anvil dummy axle and chuck it up on the lathe!

So long story short, Ken's bike is weird but should be awesome. Your bike can be awesome too if you think outside the box a bit and let me get creative - it's custom, folks. The world is your oyster.

Or we can just do 148x12, because what the heck, I already paid for the dummy axle, and the writing is on the wall...

11 comments:

Anonymous said...

So, why not just do a symetrical 150/157, rather than an offset 135/142/148?

Walt said...

Because hub selection sucks, basically. But I used to do that back when 150 was more popular (ie used on DH bikes).

It would have been nice if they'd just started using the 150x12 standard of years past, I agree. C'est la vie.

Anonymous said...

Pretty much every high end mfg makes a 150/157; including DT, King, i9, hadley and hope. And, it's still going to build a stiffer wheel than boost. Also, couldn't you just go all the way to 170 if you'll be using an 83mm shell anyway?

Walt said...

True, but they tend to be DH hubs, and then you've gotta source an axle that will work, etc. I mean, trust me, I've tried to talk people into it. They want plug and play/mainstream so my 150 and 157 dummy axles mostly gather dust.

Yes, if you look back at Kevin's low q fat bike, there's a recent example where I did 170 (symmetrical) and an 83mm shell with offset ring. Great way to get a good chainline, strong wheel, and fat tires too.

Feldy said...

By "offset ring," you mean non-offset ring, right? Since a standard ring is offset to the inside? Yes? Just sayin'.

justaute said...

My bike is not "weird", it's just "different". Quit making her, him, or it feel bad.

jgerhardt said...

How long until Ventana has "Boost" on their rear ends?

Rusty Knale said...

There are some great frames being built in MI with the 157x12 rear hub. Always interesting to see you guys thinking outside the box.

Anonymous said...

Can we keep the q factor as low as possible please? My knees will thank you.

DYG said...

Where can we see pics of Ken's complete bike built up? Sounds rad!

Johan said...

I have been looking at building offset rears (it was the Surly Pugsley that was an eyeopener in my case), but I cant figure out a way to make the crankset play nicely. The offset from the chainrings to the crankarm is too large to make a nice fit the way I would like it to be. The arms will be too wide, too far out with lots of space to the chainstays. Actually - some older square taper cranks would fit well, but I haven't seen a new crankset with suitable measurements. Any suggestions or thoughts?